Garrett <2001> points out that inertial oscillations can only propagate equatorwards. As they do so, they undergo steepening of their ray angles, and eventually the energy arrives at abyssal depths some distance equatorward of their origin. Here I show that with a given buoyancy frequency, there is a unique frequency for inertial waves that pass through any particular current meter location. Spectra from moorings off New Zealand show peaks at the predicted frequencies, and are presented in support of Garrett's theory.